(1) Field of the Invention
The present invention relates generally to blow molded floats for floating docking and, more particularly, to a method and apparatus for blow molding an asymmetrically shaped dock float having an integrally formed mounting flange and a floating dock system supported by interlocking blow molded floats.
(2) Description of the Prior Art
Hollow drums constructed of metal or plastic had been used to float docks and swim platforms for many years. Plastic drums are preferred because they do not easily rust and they resist attack by gasoline and other marine chemicals. One such drum system is shown in U.S. Pat. No. 4,799,445 issued Jan. 24, 1989 to Meriwether. This patent is hereby incorporated by reference by its entirety.
However, the means which have been used to attach plastic floats have been less than always successful because most plastic molding operations require high symmetry in the molding process. One of the most desirable geometries for attaching a float to a dock structure would be to form a mounting flange along the top of a float. This can be done relatively easily in shallow molding operations of less than about 12 inches. However, to provide maximum buoyancy, it is highly desirable to have a float depth of greater then about 20 inches.
Blow molding of thermoplastic flanged forms had been limited to forms having less than about 12 inches of depth. This is due because the amount of material that can be drawn to form a float with a flange is limited. The creation of a flange near the parting line of the mold core limits the amount of material that can be drawn into the other side of the mold. This limitation is sometimes called draw ratio or depth ratio. Blow and vacuum molding is generally limited to a depth ratio of about 4.
However, for the manufacture of high volumes of molded parts, blow molding offers substantial economic savings over other techniques of molding plastic parts. Specifically, the cycle time and labor of blow molding is substantially less than vacuum molding, twin sheet molding and rotational molding. Also, the raw materials used to form an article in blow molding are cheaper than the materials used in vacuum and twin sheet molding since solid pellets of material can be used rather than preformed sheets of material. In addition, most rotational molding operations require finely ground raw material rather than larger pellets to ensure that the material moves freely within the mold. Consequently, blow molding may be about 50 percent less expensive then competitive molding processes.
Thus, there remains a need for a new and improved molding apparatus which is able to form a flange along at least one side of a molded float while, at the same time, is able to form a molded float having a depth ratio of greater than about 4 without the thinning problems associated with such articles in the past.
The present invention is directed to a molding apparatus. The apparatus includes a preformer for supplying a predetermined amount of molten material, such as a thermoplastic resin, to an asymmetrical core. A parison former is located between the preformer and the asymmetrical core for forming a tube from the molten material. In the preferred embodiment, the parison former includes an outer die and an internal mandrel. The spacing between the outer die and the inner mandrel may be varied or asymmetrical and co-aligned with the asymmetrical core to help provide additional molten material where most needed.
The preformer may also include a pump or an extruder for preheating and sending the molten material to an accumulator which receives enough material for forming a molded article. A pusher attached to the accumulator ejects the preform from the accumulator into the open asymmetrical core.
The asymmetrical core includes a first cavity and a second, female cavity, wherein the depth ratio of the second cavity to the first cavity is greater than about 4. The first cavity may be substantially flat or include a female portion and/or a male portion such as when a waffle surface is desired to further strengthen the surface of the molded article.
A pressure differential system is connected to the asymmetrical core forming the molten material inside the asymmetrical core. The pressure differential system includes a pressurized gas source and may include a vacuum source for helping to form the molded article.
In the preferred embodiment, a movable bottom plate in the second cavity varies the depth ratio of the second cavity. This enables a molded article to be formed having a depth ratio substantially greater than 4. The movable bottom plate includes a returning means, such as a hydraulic cylinder, which may help eject the molded article and at least one stop for maintaining the movable bottom plate at a predetermined depth.
Accordingly, one aspect of the present invention is to provide a molding apparatus. The apparatus includes a preformer for supplying a predetermined amount of molten material; an asymmetrical core for receiving the molten material, wherein the asymmetrical core includes a first cavity and a second female cavity, wherein the depth ratio of the second cavity to the first cavity is greater than about 4; and a pressure differential system connected to the asymmetrical core for forming the molten material inside the asymmetrical core.
Another aspect of the present invention is to provide a core for a molding apparatus. The apparatus includes: a first cavity; a second, female cavity, wherein the depth ratio of the second cavity to the first cavity is greater than about 4; and a movable bottom plate in the second cavity for varying the depth ratio of the second cavity.
Still another aspect of the present invention is to provide a molding apparatus. The apparatus includes a preformer for supplying a predetermined amount of molten material; an asymmetrical core for receiving the molten material, wherein the asymmetrical core includes a first cavity and a second, female cavity, wherein the depth ratio of the second cavity to the first cavity is greater than about 4; and a movable bottom plate in the second cavity for varying the depth ratio of the second cavity; a pressure differential system connected to the asymmetrical core for forming the molten material inside the asymmetrical core; and a parison former located between the preformer and the asymmetrical core for forming a tube from the molten material.
The apparatus of the present invention is particularly well suited for forming a blow molded float for a floating dock system. In the preferred embodiment, the floating dock system includes a docking surface and at least one blow molded float. The blow molded float preferably has at least four sides; a thickened top mounting surface; and a bottom joined to the thickened top mounting surface by the sides. The sides, the bottom and thickened top mounting surface form an internal cavity.
Also, in the preferred embodiment, at least one of the sidewalls is substantially taper-free and an interlocking coupling means for joining a plurality of adjacent blow molded floats to one another. Preferably, the interlocking coupling means is a tongue-in-groove system and each of the blow molded floats includes the tongue-in-groove system to allow a plurality of blow molded floats to be interconnected to one another. Specifically, a first side of one of the blow molded floats includes a male tongue portion, the male portion being mateable with an opposing female groove disposed on one of the sides of an adjacent blow molded float. Because the present invention permits the sidewalls to be formed substantially taper-free, the male tongue portion and the opposing female groove are substantially taper free. Such an arrangement on tapered sidewalls would be unworkable.
The docking surface includes planking and may further include stringers for attaching the planking to the blow molded floats. The stringers may extend vertically from the planking for added strength. The docking surface may also include sheeting instead of planking. Preferably, adjacent pieces of the sheeting are joined along at least one common interlocking edge. In either case, the docking surface is selected from a variety of water and weather resistant materials, such as marine plywood, rigid plastic sheeting, a vinyl sheet or a composite.
Because of symmetry requirements, the blow molded float is preferably a rectangular-shaped, hollow solid. More preferably, the blow molded float has a width dimension of about 2 feet, a length dimension of about 4 feet and a depth of about 20 inches. This allows pairs of blow molded floats to form a 4 foot by 4 foot surface useful, for example, for a swimming rest float.
In the preferred embodiment, the thickened top mounting surface further includes an integrally molded flange, the integrally molded flange extending horizontally beyond at least one of the sidewalls. Such an arrangement has not been previously possible, as will become apparent below. The integrally molded flange extends horizontally beyond at least two of the sidewalls and, preferably, extends horizontally beyond at least three of the sidewalls. This overlapping U-shape allows a string of floats to be attached to one another.
Blow molded objects are inherently air tight unless punctured but this can easily happen to a floating dock. Accordingly, in the preferred embodiment, the cavity is filled with a low-density filling such as closed cell, expandable polystyrene foam.
The thickened top mounting surface may further include ribbing to prevent warping of the thickened top mounting surface during molding and a utility channel or channels.
Accordingly, one aspect of the present invention is to provide a floating dock system. The floating dock system includes a docking surface; and at least one blow molded float, the blow molded float having at least four sides; a thickened top mounting surface; and a bottom joined to the thickened top mounting surface by the sides, wherein the sides, the bottom and thickened top mounting surface form an internal cavity.
Another aspect of the present invention is to provide a floating dock system. The floating dock system includes a docking surface; and at least one blow molded float, the blow molded float having at least four sides; a thickened top mounting surface; and a bottom joined to the thickened top mounting surface by the sides, wherein the sides, the bottom and thickened top mounting surface form an internal cavity and wherein at least one of the sidewalls is substantially taper-free.
Still another aspect of the present invention is to provide a floating dock system. The floating dock system includes a docking surface; at least one blow molded float, the blow molded float having at least four sides; a thickened top mounting surface; and a bottom joined to the thickened top mounting surface by the sides, wherein the sides, the bottom and thickened top mounting surface form an internal cavity and wherein at least one of the sidewalls is substantially taper-free; and an interlocking coupling means for joining a plurality of adjacent blow molded floats to one another.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.